1. Field of the Invention
The present invention relates to an apparatus for measuring a state of charge of, for example, a battery device and particularly relates to a technique for correcting the state of charge of the battery obtained by calculation based on integrated electric current.
2. Description of the Related Art
When measuring a state of charge (SOC) of a battery, provided, for example, in a hybrid vehicle, the following method is known as a typical method, in which, since the state of charge is proportional to the total amount of charge stored in the battery, a total amount of charge and a total amount of discharge are first calculated by integrating a charge current and a discharge current detected for each predetermined period of time, and the state of charge of the battery can then be obtained by addition or subtraction of the integrated quantity of charge and the integrated quantity of discharge to or from an initial state of the battery or the initial state of charge of the battery immediately before starting charge and discharge.
However, the above method has a drawback in that, when obtaining the state of charge by measuring the integrated quantity of charge and the integrated quantity of discharge, the error contained in the calculated state of charge of the battery increases because errors in measurements of the charge current or the discharge current by the current detector in every current measurement is integrated.
In order to obtain an accurate value of the state of charge by the above total current integration method, Japanese Unexamined Patent Application, First Publication No. Hei 6-6901 proposes a battery state of charge measuring apparatus. The proposed detecting device first calculates an electrical consumption after correcting a standard consumption obtained by integrating the discharge current of the battery by multiplying each correction coefficient in response to battery terminal voltage, density, temperature, and discharge current, and the state of charge is calculated by obtaining a difference value obtained by subtracting the above electrical consumption from the initial charge of the battery and then by correcting the difference value by multiplying respective correction coefficients regarding a quantity of charge, a quantity of discharge before charging, the number of times of charging, a temperature at charging, and so on.
In the aforementioned state of charge measuring apparatus according to one example of the conventional techniques, various correction coefficients are employed obtained by previously stored predetermined relational equations or maps. Since these relational equations and maps are prepared according to characteristic properties at a predetermined state of the battery, for example, stable properties at a stationary state of the battery, a problem arises that the estimated state of charge of the battery obtained by the predetermined relational equations or maps may be separated from an actual value, when a storage capacity of the battery has been changed due to long term use or when the battery is replaced with a different type battery.
As described above, when the state of charge of the battery contains an error, there is a possibility to set a state of charge which differs from the controllable range of the battery, which may results in shortening of the service life of the battery or result in causing defective control of the motor or the engine.
The present invention has been made to solve the above problems and an object of the present invention is to provide a battery state of charge measuring apparatus, capable of obtaining an accurate state of charge of a battery based on a value obtained by integrating charge and discharge currents, even when the battery properties have been changed after a long-term use or even when the battery has been replaced.
The first aspect of the present invention provides a state of charge measuring apparatus for a battery device comprising a battery (for example, a battery 14 in the embodiment shown below), a load (for example, a motor M in the embodiment shown below) driven by electrical power supplied from the battery device, and a state of charge calculating device (for example, integrated state of charge calculating portion 32 in the embodiment shown below) for detecting a charge and discharge currents (for example, charge and discharge currents I in the embodiment shown below) of the battery device and for calculating an integrated state of charge of the battery device (for example, integrated SOC in the embodiment shown below) based on an integrated value (for example, a consumed charge Q in the embodiment shown below) of charge and discharge currents, comprising a voltage detecting device (for example, a voltage detector 16 in the embodiment shown below) for detecting a terminal voltage (for example, a terminal voltage V in the embodiment shown below) of the battery, an upper limit substitution device (for example, an upper and lower limit substitution device 33 in the embodiment shown below) for substituting the integrated state of charge value to an upper limit state of charge (for example, an upper limit SOC in the embodiment shown below) when a detected voltage obtained by the terminal voltage detecting device exceeds a predetermined voltage (for example, an upper limit voltage VU in the embodiment shown below), and a decreasing side corrected state of charge calculating device (for example, corrected state of charge calculating portion 35 in the embodiment shown below) for calculating a corrected state of charge (for example, corrected SOC in the embodiment shown below) by correcting the integrated state of charge after the data substitution when the state of charge of the battery is decreasing, wherein the decreasing side corrected state of charge calculating device (for example, the corrected state of charge calculating portion 35 in the embodiment shown below) corrects such that a difference between the integrated state of charge and the corrected state of charge increases as the integrated value of the charge and discharge currents increases.
By constructing the state of charge measuring apparatus as shown above, the integrated state of charge data can be substituted to a predetermined upper limit in response to the terminal voltage, and a correction processing is carried out such that a difference between the integrated state of charge obtained after the data substitution and the corrected state of charge after correcting the integrated state of charge increases with the integrated value of the charge and discharge currents.
Even when a difference between the integrated state of charge and the actual state of charge increases as the integrated value of the charge and discharge currents increases, it is possible to improve the accuracy for approximating the corrected state of charge to the actual state of charge.
According to the second aspect, the state of charge measuring apparatus for a battery device comprising a battery device (for example, a battery 13 in the embodiment shown below), a load (for example, a motor M in the embodiment shown below) driven by electrical power supplied from the battery device and a state of charge calculating device (for example, an integrated state of charge calculating device 32 in the embodiment shown below) for detecting a charge current and discharge currents (for example, charge and discharge currents I in the embodiment shown below) of the battery device and for calculating an integrated state of charge of the battery based on an integrated value (for example, a consumed charge Q in the embodiment shown below) of the charge and discharge currents, comprising, a voltage detecting device (for example, a voltage detector 16 in the embodiment shown below) for detecting a terminal voltage (for example, a terminal voltage V in the embodiment shown below) of the battery device, an lower limit substitution device (for example, a upper and lower limit values substitution portion 33 in the embodiment shown below) for substituting the integrated state of charge value to an lower limit state of charge when a detected voltage obtained by the terminal voltage detecting device falls below a predetermined voltage (for example, a lower limit SOC in the embodiment shown below), and an increasing side corrected state of charge calculating device (for example, a corrected state of charge calculating portion 35 in the embodiment shown below) for calculating a corrected state of charge by correcting the integrated state of charge after the data substitution when the state of charge of the battery is increasing, wherein the increasing side corrected state of charge calculating device corrects such that a difference between the integrated state of charge and the corrected state of charge increases as the integrated value of the charge and discharge currents increases.
By constructing the state of charge measuring apparatus as shown above, the integrated state of charge data can be substituted to a predetermined lower limit in response to the terminal voltage, and a correction processing is carried out such that a difference between the integrated state of charge obtained after the data substitution and the corrected state of charge after correcting the integrated state of charge increases as the integrated value of the charge and discharge currents.
Even when a difference between the integrated state of charge and the actual state of charge increases as the integrated value of the charge and discharge currents increases, it is possible to improve the accuracy for approximating the corrected state of charge to the actual state of charge.
According to the third aspect, in the above state of charge measuring apparatus for a battery device, the battery state of charge measuring apparatus further comprises an upper limit substitution value calculating device (for example, an upper and lower limit substitution value calculating portion 34 corrected state of charge calculating portion 35 in the embodiment shown below) for calculating a substitution value (for example, (upper limit SOCxe2x88x92lower limit SOC) in the embodiment shown below) from the integrated state of charge to the upper limit value by a difference between the integrated state of charge and the upper limit value, and the decreasing side corrected state of charge calculating device comprises a correction value incrementing device (for example, a correction value adding portion 36 in the embodiment shown below), provided to be used when the correction value exceeds a predetermined correction value while defining a first unit correction value (for example, a unit correction value B0 in the embodiment shown below) used as a correction value for one time data substitution, for incrementing the correction value (for example, a correction value A in the embodiment shown below) by adding a first unit correction value each time the data substitution is repeated.
By constructing the state of charge measuring apparatus as shown above, the correction value is incremented as the number of correcting time increases, and the difference between the corrected state of charge calculated by the above correction value and the integrated state of charge calculated after the data substitution increases.
Accordingly, as the number of times of data substitution increases, the corrected state of charge can be approximated in a more accurate manner.
According to the fourth aspect, the above state of charge measuring apparatus for a battery device comprises a lower limit substitution value calculating device (for example, the upper and lower limit substitution amount calculating device 34 shown below in the embodiment) for calculating a substitution value (for example, (data substitution time integrated SOCxe2x88x92lower limit SOC) in the embodiment shown below) for substituting from the integrated state of charge to the lower limit based on a difference between the integrated state of charge and the lower limit value, wherein the increasing side correction state of charge incrementing device defines a first predetermined unit correction value (for example, unit correction value B0 in the embodiment shown below) as a value (for example, a correction value A in the embodiment shown below) for correcting at one correction time, when the substitution value is greater than a predetermined value (for example, (unit correction value B0+previous correction value) in the embodiment shown below) and increases the correction value by adding said first unit correction value each time when the data substitution is performed.
By constructing the state of charge measuring apparatus as shown above, the correction value is incremented as the number of correcting time increases, and the difference between the corrected state of charge calculated by the above correction value and the integrated state of charge calculated after the data substitution increases.
Accordingly, as the number of times of data substitution increases, the corrected state of charge can be approximated in more accurate manner.
According to the fifth aspect, the correction value incrementing device adjusts the correction value to the same value as that of the substitution value when a difference between the substitution value and the added corrected value is less than the first unit correction value.
By constructing the state of charge measuring apparatus as shown above, the corrected state of charge is calculated based on the substitution value, which is obtained from the difference between the integrated state of charge and the lower limit value of the state of charge or the difference between the integrated state of charge and the upper limit state of charge.
According to the sixth aspect, in the above state of charge measuring apparatus for a battery device, when a difference between the substitution value and the added corrected value is less than the first unit correction value, the correction value incrementing device corrects the state charge of the battery device using a correction value that is a sum of the second unit correction value, which is less than the first unit correction value, and the corrected value obtained until the previous time.
According to the above state of charge measuring apparatus of the battery device, the correction state of charge is obtained as a sum of the second unit correction value and the correction value obtained until the previous correction time.
The correction state of charge obtained by this aspect is more closer to the required correction value than when the correction state of charge is obtained by use of the first unit correction value.
According to the next aspect of the present invention, the state of charge measuring apparatus for a battery device comprises a display device for displaying said corrected state of charge.